Summary of Work: Certain NCI protocol patients are imaged repetitively over the course of many days or weeks. For several reasons, it is desirable to be able to (l) align the images from one imaging session to another and (2) align the two-dimensional (2-D) nuclear medicine projection images with computer tomography (CT) images of the same subject. Alignment of projection images from one imaging session to another permits more accurate quantitation of changes in uptake over time. Aligning scans done on subsequent days also permit a single transmission scan to be used to perform absolute quantitation. Alignment of the nuclear medicine projection images with the CT data permits correlation of radio-pharmaceutical uptake with morphological structure. In addition, the CT data may themselves be used to perform attenuation correction of the emission data. An investigation of alignment scheme (1) has been performed, using an adaptation of a technique previously published by our group for three-dimensional alignment of positron emission tomography data. The method was modified for alignment of 2-D projection images and uses maximal pixel-to-pixel correlation techniques, applied to the transmission scan. The method uses lung borders to optimize the alignment. The method has now been thoroughly tested on phantoms and with simulated and actual motion of patient data, and a manuscript is being prepared for publication. In addition, further clinical testing, using markers visible on both CT and nuclear medicine single photon emission computed tomography scans is being performed.